H-Hour approaches for state Education Commissioner John King — for his professional credibility, for his personal reputation, maybe even for his soul.

It has fallen to King, by all accounts an honorable man, to settle by Saturday an issue that has vexed New York for years. Namely: how to get the state’s politically potent teachers unions to accept personal accountability as a bedrock principle of public-education reform.

On the one side there is Gov. Cuomo, the self-described “top lobbyist” for the state’s students, and Mayor Bloomberg — who has made as heroic an effort to fix the city’s schools as can be imagined, but who now watches the calendar run out on his mayoralty with that task far from finished.

On the other is United Federation of Teachers President Michael Mulgrew, intransigence personified, and his predecessor, now-American Federation of Teachers honcho Randi Weingarten, who once seemed to have a conscience on such matters — but no more.

Mulgrew and Weingarten decorate their rhetoric with filigrees of reform, but they are as inflexible as matched blocks of granite: No tenured teacher, under any circumstances, is to be held to account for any failing of any sort — forever and ever, amen.

Then there is the moral cesspit of New York politics, a fetid amalgam of purchasable elected officials and purpose-built “grass-roots groups” — shameless in their lust for UFT dollars and organizational support, and utterly contemptible in their disregard for the best interests of 1.1 million public-school pupils.

So who can envy John King? By law, he has until Saturday to promulgate regulations for “evaluating” the classroom fitness of the city’s 75,000-plus teachers — that is, to impose a template for accountability that has eluded genuine reformers for years.

Tugging at King from one side is the knowledge that if he fails, millions of children will, over time, pay the price. Does his conscience nag?

Tearing fiercely at him from the other direction are the forces vested in the status quo — which, again, cares nothing for the children. Nothing at all.

It must have been particularly painful for King to stand by and watch his patron, state Board of Regents Chancellor Merryl Tisch, slide into the pit.

But slide she did, turning her back on an implied moral obligation to avoid partisan politics — and vesting the power and prestige of her office in an endorsement of William Thompson for mayor.

And not just an endorsement. The most powerful person in New York education — the woman who appointed King to his job — is co-chairing Thompson’s campaign. Next month, she’ll co-host a fund-raiser for the former comptroller with Randi Weingarten herself.

Let’s be clear: The union insists that non-accountability inform any evaluation deal, and it wants that deal before it endorses a mayoral candidate, now set for mid-June.

So could Tisch’s conflict of interest be any more obvious? Could her message to King be any more explicit?

Hardly.

Clouds of smoke will be generated between now and Saturday. And there is always the (remote) possibility of an agreement between the union and Bloomberg’s negotiators before the deadline.

But once a resolution is announced, and the spinning begins, how best to tell who won, and who lost? Whether there’ll be reform, or regression?

Here’s some hints:

* If the UFT threatens a lawsuit, King did the right thing.

* If the union’s scavenger allies — e.g., the NAACP and the e-mail-address-only “New Yorkers for Great Public Schools” — set to grousing, ditto.

* But if the union and its acolytes praise King for his leadership and statesmanship, the commissioner caved.

* And if Mulgrew and Bloomberg appear jointly, deploying words like “fair,” “reasonable,” “prudent” and “compromise,” King littered his decision with fig-leaves behind which everybody can hide — but the kids will have lost nevertheless. There will be no accountability.

At the moment — two days out from the deadline — all those kids have going for them is John King’s integrity. He’s a very lonely man, with a very rare opportunity, who is going to have to face his shaving mirror for a very long time to come.

Pray that he does the right thing — for the children, of course, but for his own sake as well. For his soul.